I look at it this way; if I went out and bought plates of 3/16" - 1/4" steel it would cost X amount. If I needed to buy a plasma or acetylene torch to cut the steel it would cost X amount. Then I would need to have a welder. Then I would need some amount of engineering or years of experience to make sure it works and I won't be sued. Then I would get them powdered coated and it would cost me a lot more than I paid Torklift or Happijac.
I do know there are talented welders on the forum that could do it for a LOT less...but I'm not one of them.
Or you could check out Craigslist and see if you can find used ones for sale.